NOVEL COMPLEXES FOR THE SEPARATION OF CATIONS

Abstract

Complexes including a solid support and a material with a matrix structure containing domains complexing rare earth or strategic metals, preparation process thereof and use thereof for extracting or separating the rare earth or strategic metals in an aqueous or organic medium.

Claims

1. Complex comprising (i) a solid support and (ii) a solid material with a homogeneous matrix structure, having a structuring element and a cross-linking element, said material being at least insoluble in water or in an organic solvent and capable of being swelled by water or said organic solvent, at least one of the two elements bearing or forming a complexing domain of strategic metals constituted by the rare earths, antimony, indium, beryllium, magnesium, cobalt, niobium, the platinoids, gallium, germanium, tantalum, tungsten, molybdenum, titanium, mercury, cesium, lithium and strontium, in particular the rare earths, said structuring element and said cross-linking element being formed, independently of one another, by at least one entity selected from the group consisting of: (a) a polymer constituted by monomers, said polymer optionally bearing at least one coordinating group, advantageously a phosphate group, (b) a cage molecule, (c) a linear or branched (C.sub.1-C.sub.15) alkyl, optionally substituted by at least one substituent selected from: a (C.sub.1-C.sub.5) alkoxy group, a carbonyl group, an aryl group or a substituted aryl group, such as a tosyl group, a diazonium group, an aromatic heterocycle such as a pyrrolyl, furyl, thienyl or pyridinyl group, a sulphur atom, a sulphate or sulphonate group, a phosphate group, (d) a linear or branched (C.sub.2-C.sub.1) alkenyl or alkynyl, optionally substituted by at least one substituent selected from: a (C.sub.1-C.sub.5) alkoxy group, a carbonyl group, an aryl group or a substituted aryl group, such as a tosyl, a diazonium group, an aromatic heterocycle such as a pyrrolyl, furyl, thienyl or pyridinyl group, a sulphur atom, a sulphate or sulphonate group, a phosphate group, and (e) an aryl(C.sub.1-C.sub.15)alkyl group, optionally substituted by at least one substituent selected from: a (C.sub.1-C.sub.5) alkoxy group, a carbonyl group, an aryl group or a substituted aryl group, such as a tosyl, a diazonium group, an aromatic heterocycle such as a pyrrolyl, furyl, thienyl or pyridinyl group, a sulphur atom, a sulphate or sulphonate group, a phosphate group, said cross-linking element being cross-linked with said structuring element by one or more bonds selected from the group consisting of: C(O)NH, NH, C(O), CS, CN, S, SO.sub.3, CC, CO, provided that, when said complexing domain is not formed by a cage molecule, then said structuring element, or said cross-linking element or both bear at least one coordinating group, advantageously a phosphate group.

2. Complex according to claim 1, wherein said structuring element and said cross-linking element are formed by an entity selected from (a) a polymer constituted by monomers and (b) a cage molecule, said structuring element being different from said cross-linking element.

3. Complex according to claim 1, wherein the polymer constituted by monomers is selected from an acrylic acid-based polymer, in particular an acrylic acid homopolymer, or a polymer based on 4-vinylpyridine, in particular a poly(4-vinylpyridine).

4. Complex according to claim 1, wherein the cage molecule is selected from the group comprising the calix[n]arenes in which n is an integer from 4 to 100, advantageously from 4 to 50, preferentially from 4 to 8, the crown ethers and the cyclodextrins.

5. Complex according to claim 1, wherein said structuring element of said complex is formed by a calix[n]arene in which n is an integer from 4 to 100, advantageously from 4 to 50, preferentially from 4 to 8, and said cross-linking element of said complex is formed by a poly(4-vinylpyridine).

6. Complex according to claim 1, wherein said structuring element of said complex is formed by a poly(4-vinylpyridine) and said cross-linking element of said complex is formed by a calix[n]arene in which n is an integer from 4 to 100, advantageously from 4 to 50, preferentially from 4 to 8.

7. Method for the preparation of a complex according to claim 1, said method comprising: a first step of bringing a liquid mixture or a solid, comprising an agent capable of structuring and an agent capable of cross-linking, into contact with a surface of a solid support, at least one of the two agents bearing a complexing domain or being capable of forming a complexing domain after cross-linking, for strategic metals constituted by the rare earths, antimony, indium, beryllium, magnesium, cobalt, niobium, the platinoids, gallium, germanium, tantalum, tungsten, molybdenum, titanium, mercury, cesium, lithium and strontium, said agent capable of structuring and said agent capable of cross-linking being identical or different and corresponding to formula R.sub.1-L-R.sub.2, in which: (i) L is selected from the group consisting of: (a) a polymer, optionally substituted by at least one functional group selected from: a coordinating group, advantageously phosphate, an amine, optionally protected by an amine protective group, a halogen selected from F, Cl, Br, I, OH, C(O)H, C(O)Hal in which Hal represents a halogen atom, a tosyl group, a sulphate or sulphonate group, optionally protected by a protective group of the sulphate or sulphonate group, a thiol, optionally protected by a protective group of the thiols (b) a cage molecule, optionally substituted by at least one functional group selected from: a phosphate group, an amine, optionally protected by an amine protective group, a halogen selected from F, Cl, Br, I, OH, C(O)H, C(O)Hal in which Hal represents a halogen atom, a tosyl group, a sulphate or sulphonate group, optionally protected by a protective group of the sulphate or sulphonate group, (c) a linear or branched (C.sub.1-C.sub.15) alkyl, optionally substituted by at least one substituent selected from: an alkoxy group, a carbonyl group, such as C(O)H, and C(O)Hal in which Hal represents a halogen atom, an aryl group or a substituted aryl group, such as a tosyl group, a diazonium group, an aromatic heterocycle such as a pyrrolyl, furyl, thienyl, pyridinyl group, a sulphate or sulphonate group, optionally protected by a protective group of the sulphate or sulphonate group, an amine, optionally protected by an amine protective group, a halogen selected from F, Cl, Br, I, OH, a phosphate group, a thiol, optionally protected by a protective group of the thiols (d) a linear or branched (C.sub.2-C.sub.15) alkenyl or alkynyl, optionally substituted by at least one functional group selected from: an alkoxy group, a carbonyl group, such as C(O)H and C(O)Hal in which Hal represents a halogen atom, an aryl group or a substituted aryl group, such as a tosyl group, a diazonium group, an aromatic heterocycle such as a pyrrolyl, furyl, thienyl or pyridinyl group, a sulphate or sulphonate group, optionally protected by a protective group of the sulphate or sulphonate group, an amine, optionally protected by an amine protective group, a thiol, optionally protected by a protective group of the thiols a halogen selected from F, Cl, Br, I, OH, a phosphate, (e) a linear or branched aryl(C.sub.1-C.sub.15)alkyl, optionally substituted by at least one functional group, preferentially at least 2 functional groups, selected from: an alkoxy group, a carbonyl group, such as C(O)H, and C(O)Hal in which Hal represents a halogen atom an aryl group or a substituted aryl group, such as a tosyl group, a diazonium group, an aromatic heterocycle such as a pyrrolyl, furyl, thienyl or pyridinyl group, a sulphate or sulphonate group, optionally protected by a protective group of the sulphate or sulphonate group, an amine, optionally protected by an amine protective group, a halogen selected from F, Cl, Br, I, OH, a phosphate, a thiol, optionally protected by a protective group of the thiols (ii) R.sub.1 and R.sub.2 being selected from the group comprising: an amine, optionally protected by an amine protective group, a halogen selected from F, Cl, Br, I, OH, C(O)H, C(O)Hal, a tosyl group or an aryldiazonium group, a sulphate or sulphonate group, optionally protected by a protective group of the sulphate or sulphonate group, a thiol, optionally protected by a protective group of the thiols a hydrogen, the R.sub.1, R.sub.2 groups or the functional groups borne by L of an agent capable of cross-linking being selected so that they are capable of reacting with the R.sub.1, R.sub.2 groups or the functional groups borne by L of an agent capable of structuring so as to allow cross-linking between said structuring and cross-linking agents; and a second step of formation of a solid material with a homogeneous matrix structure as previously defined, by heat treatment, at a temperature comprised between 20 C. and 200 C., of an aforesaid liquid or solid mixture comprising an agent capable of structuring and an agent capable of cross-linking on the aforesaid support.

8. Complex obtained by implementing the method according to claim 7.

9. Method for extracting or separating, from an aqueous or organic medium, strategic metals constituted by the rare earths, antimony, indium, beryllium, magnesium, cobalt, niobium, the platinoids, gallium, germanium, tantalum, tungsten, molybdenum, titanium, mercury, cesium, lithium and strontium, said method comprising the step of: (i) placing an aqueous or organic medium in contact with a complex according to claim 1.

10. Method according to claim 9, also comprising after step (i), a step of recovering strategic metals, in particular rare earths, retained in the aforesaid complex.

11. Phosphorylated calixarene of formula I: ##STR00011## in which: X.sub.1 and X.sub.2 each represent, independently of one another, H or a ##STR00012## group, in which R.sub.3 and R.sub.4 each represent, independently of one another, H or a (C.sub.1-C.sub.8) alkyl group, provided that X.sub.1 and X.sub.2 do not simultaneously represent H, L.sub.1, L.sub.2, L.sub.3 et L.sub.4 are spacer groups, selected independently of one another from the group consisting of a (C.sub.3-C.sub.10) cycloalkylenyl group, O, NH, (CH.sub.2).sub.q, q being an integer from 0 to 12, or from 1 to 12, Z.sub.1 et Z.sub.2 each represent, independently of one another, a functional group selected from an optionally protected amine group, F, Cl, Br, I, OH, C(O)H, C(O)Hal, an aryl group or a substituted aryl group, such as a tosyl group, a diazonium group, an aromatic heterocycle such as a pyrrolyl, furyl, thienyl or pyridinyl group, an optionally protected sulphate or sulphonate group, or a ##STR00013## group, in which R.sub.3 et R.sub.4 are as defined above, Z.sub.1 et Z.sub.2 not both being in the ##STR00014## group, n being an integer from 4 to 100.

12. Phosphorylated calixarene of formula I according to claim 11 for the preparation of a complex whose structuring element is formed by a poly(4-vinylpyridine) and said cross-linking element of said complex is formed by a calix[n]arene in which n is an integer from 4 to 100.

Description

[0285] The present invention is illustrated by FIGS. 1 to 6 and the following Examples 1 to 5.

[0286] FIG. 1 shows the matrix of a material according to the invention, in which the structuring element is formed by cage molecules (C).

[0287] FIG. 2 shows the matrix of a material according to the invention, in which the complexing domain for a molecule of interest (M) is formed by the structuring element.

[0288] FIG. 3 shows the matrix of a material described in the invention, in which the structuring element is formed by a polymer; the cross-linking element is formed by the cage molecules.

[0289] FIG. 4 shows the retention of europium by the KT103-P4VP carbon felt complex (b) and c)) or by a reference complex (a) as measured according to Example 2. The presence of europium is detected by X-ray photo-electron spectroscopy.

[0290] FIG. 5 shows the IR transmittance as a function of the wavelength of an AAP-calix-gold complex obtained by heat treatment according to Example 4. Spectrum (a) is recorded just after the deposition and drying of the alcohol. Spectrum (b) is recorded after baking at 200 C. Spectrum (c) is obtained after of hydrolysis for 10 minutes at pH10. Spectrum (d) is obtained after rapid rinsing of an initial film with water.

[0291] FIGS. 6A and 6B show a complex of the invention constituted by a carbon felt covered by a three-dimensional matrix material, before (FIG. 6A) and after (FIG. 6B) contact with water, clearly demonstrating the swelling of said material.

EXAMPLE 1: EXTRACTION OF CESIUM BY A KT101-P4VP-CARBON FELTS COMPLEX

(i) Synthesis of 1,3-alternate-diiodobutyl calix[4]arene-crown-6 (KT101)

[0292] The calixarene KT101 is synthesized according to the chemical reaction illustrated below:

##STR00008##

(i) Preparation of KT101

[0293] 200 mg of calixarene 49 (0.248 mmol) and 81.72 mg of NaI (0.545 mmol) are dissolved in 6 mL of 2-butanone and under stirring for 48 h at 80 C.

[0294] After the reaction, the solvent is evaporated off under vacuum. The residue obtained is extracted 3 times with 30 mL of dichloromethane. The organic layer obtained is washed once with 60 mL of salt water and then filtered through celite. 76 mg of KT101 (ESI-MS m/z 1013.19 (M+Na).sup.+) are obtained in the form of white powder after filtration under vacuum.

(ii) Preparation of the KT101-P4VP-Carbon Felt Complex

[0295] 76 mg of KT101 and 50 mg of poly(4-vinylpyridine) (P4VP) are dissolved in 5 ml of distilled THF. The reaction mixture thus obtained is heated under reflux at 80 C. for 72 h in order to form N-calixpyridinium iodide with the formula below:

##STR00009##

[0296] The carbon felts (Mersen) in form of a disk with a diameter of 2 cm are immersed in said reaction mixture containing the aforesaid N-calixpyridinium iodide in a quantity of 10.sup.3 M-10.sup.4 M in order to extract the element of interest present at a concentration of 10.sup.3 M-10.sup.4 M in an aqueous solution used as a model of the effluent. They are then baked in an oven at 100 C. for 8 h in order to complete the cross-linking reaction.

[0297] At the end of this step, the carbon felts are obtained covered with P4VP polymer cross-linked with KT101.

(iii) Treatment of Effluents Containing Cesium Salt

[0298] After rinsing with water and drying at 100 C., the KT101-P4VP-carbon felts complex obtained in step (ii) is subjected to a competitive test in order to assess the effectiveness and specificity of said complex for the extraction of cesium.

[0299] Aliquots of approximately 0.9 g originating from 3 disks of carbon felt obtained in step (ii) are immersed, for 20 minutes or 5 days, at ambient temperature, in a solution of 20 ml of concentrations approximately 10.sup.4 M of cesium nitrate and approximately 0.1 M of sodium nitrate. This solid phase constituted by carbon felt loaded with polymer bearing calixarenes at a concentration that makes it possible to have an extraction percentage comprised between 10 and 90%.

[0300] The cesium concentrations, at the start (C.sup.i) and at the end of the treatment (C.sup.f), are determined by atomic absorption spectrometry.

[0301] The results are illustrated in Table 1 below.

TABLE-US-00001 TABLE 1 after 20 min after 5 days Final concentration Cs after 0.085 0.069 treatment with P4VP-KT101, (C.sup.f, mM) Initial concentration Cs (C.sup.i, 0.223 0.222 mM) % E* 61.88 68.91 *% E is the extraction percentage of cesium determined according to the formula: % E = (C.sup.i C.sup.f)/C.sup.i 100%, in which C.sup.i and C.sup.f are respectively the concentration of cesium before and after extraction.

[0302] These results show that the KT101-P4VP-carbon felts complex of the invention effectively and specifically extract the cesium present in a effluent.

EXAMPLE 2: EXTRACTION OF EUROPIUM BY A KT103-P4VP-CARBON FELTS COMPLEX

(i) Synthesis of a Mixture of Phosphorylated Calixarenes

[0303] Phosphorylated calixarenes are synthesized according to the following reaction steps:

##STR00010##

[0304] The calixarene 5,17-dibromo-25,27-bis(4-chlorobutoxy)calix[4] arene (denoted hereafter KT 102) is obtained by the direct addition of bromine atoms onto the calixarene KT46 according to the method described by Guillon et al. (Supramolecular Chemistry, 2004, 16, 319). KT 102 is then subjected to an Arbuzov reaction catalyzed by NiBr.sub.2, in order to produce a mixture of two phosphorylated calixarenes, namely compound Ia and compound Ib, together named the KT103 series is used as it is in the following reactions without further purification.

[0305] The composition of the KT103 mixture is confirmed by MALDI-TOF spectrometry. The spectrum of said mixture shows two respective peaks at m/z=1065.20 and at m/z=1195.29, corresponding to two ionic complexes formed by two compounds of the KT103 mixture with cesium trifluoroacetate (CsTFA).

(ii) Preparation of the KT103-P4VP-Carbon Felt Complex

[0306] The mixture of calixarenes KT103 and poly(4-vinylpyridine) (P4VP) is dissolved in distilled THF (5 ml of solvent for 0.5 mmol of calixarene and 1.9 mmol of P4VP). The reaction mixture thus obtained is heated under reflux at 80 C. for 72 h in order to form N-calixpyridinium chlorides.

[0307] The reaction medium is deposited by immersion as described in the preceding example on carbon felts (Mersen) in the form of disks with a diameter of 2 cm in a sufficient quantity to extract the element of interest present at a concentration of 10.sup.3 M-10.sup.4 M in an aqueous solution used as a model of the effluent. Then the carbon felts are baked in an oven at 100 C. for 8 h in order to complete the cross-linking reaction.

[0308] After the heat treatment, the carbon felts are rinsed in deionized water for 8 h at ambient temperature in order to confirm the insolubility of the P4VP-KT103 polymer in an aqueous medium.

(iii) Preparation of a Reference Complex Based on P4VP

[0309] A reference complex consisting of a gold plate coated with a P4VP polymer cross-linked with diiodohexane is prepared according to the same method. The cross-linked polymer is deposited on a gold plate, washed with ethanol then with deionized water and dried in an oven for 8 h at 100 C.

(iv) Treatment of a Solution Simulating an Effluent Containing Europium Salt

[0310] Approximately 0.9 g of carbon felts (3 disks with a diameter of 2 cm) obtained in step (ii) are immersed, for 20 minutes, at ambient temperature in 20 ml of a solution of containing approximately 10.sup.3 M of europium nitrate. The carbon felts are then rinsed with ethanol in order to remove the non-complexed metallic ions and dried in an oven. The europium retained by the KT103-P4VP-carbon felt complex is analyzed by XPS (X-ray photoelectron spectrometry).

[0311] The comparative experiment is carried out with the reference complex prepared according to Example 2 (iii).

[0312] The respective spectra of the KT103-P4VP-carbon felt complex and of the reference complex are shown in FIG. 4.

[0313] Unlike the reference complex which does not absorb the europium and on which the presence of these ions is not observed, the KT103-P4VP-carbon felt complex retains the europium ions contained in the test solution.

EXAMPLE 3: EXTRACTION OF THE CESIUM BY A AAP-CALIX-CARBON FELT COMPLEX

(i) Preparation of the AAP-Calix-Carbon Felt Complex by Gamma Radiation Treatment

[0314] A solution of polyacrylic acid (AAP) is prepared with 50 mg in 10 ml of ethanol. A solution of 25,27-bis(4-chlorobutoxy)calix[4]arenes-crown-6 (calixarene 49) is prepared with 11 g in 40 ml of DMSO (dimethylsulphoxide).

[0315] The final solution is made by adding 600 l of the solution of calix 49 in 10 ml of solution of AAP (i.e. approximately 5 mg of AAP for 16.5 mg of calix 49 per millilitre of solution). The mixture is left under stirring for 30 minutes in order to clarify it.

[0316] Disks of carbon felt (RVG 40000.7 m.sup.2/gd=0.088) with a diameter of 2.8 cm (340 mg) are subjected to an ArO.sub.2 [90-10%] plasma treatment for 10 minutes in order to wet them. This treatment limits recession of the liquid during drying and makes it possible to obtain coatings covering all of the fibres.

[0317] A solution of polyethylene imine (PEI), having a molecular weight of 25,000, is prepared by the dissolution of 5 mg of PEI in 10 ml of deionized water.

[0318] A first impregnation of the disks of carbon felt is carried out with an aqueous solution of polyethylene imine (PEI) at 5 mg/10 ml.

[0319] The felt is filled using a Pasteur pipette until visual detection that the impregnation is complete. Then the felt is left to dry. The primary coating of PEI (polymer having positive charges) reinforces the polyelectrolytic properties of the AAP (negatively charged) and leads to a better coating of the fibres.

[0320] A second impregnation is carried out with the solution of AAP and calixarene described above until visual detection that the impregnation is complete. The felt is left to dry naturally.

[0321] The gamma irradiation is carried out for 8 h in a gammacell 3000 Elan with 662 keV photons (5.5 Gy/min).

[0322] Repeated rinsing with water or with basic solutions (pH=9-10) do not make it possible to remove the interferential stains visible on the carbon fibres. The AAP coatings are therefore immobilized on the fibres.

[0323] The control samples (in which the calixarene 49 is not added) are prepared according to the same process.

(ii) Treatment of a Solution Containing Cesium Salt

[0324] Analysis of the selective extraction of cesium from an aqueous solution containing chloride ions is carried out according to the following method:

[0325] 3 felts prepared according to step (i), as well as the control felts coated with AAP, are introduced respectively into a pill bottle with a stopper and covered with 20 ml of a solution of 0.2 mM/10 mM of Cs+/Na+ in tap water; they are left for 20 min at ambient temperature while stirring regularly. The cesium molar concentrations of the samples was then measured by flame absorption spectroscopy.

[0326] The results are illustrated in Table 2 below.

TABLE-US-00002 TABLE 2 Sample Concentration (mmol/ml) Initial solution 0.255 Solution after contact with AAP- 0.191 calix-carbon felts complex

[0327] The result shows that the AAP-calix-carbon felts complex makes it possible to extract the cesium cation.

EXAMPLE 4: PREPARATION OF THE AAP-CALIX-GOLD COMPLEX BY HEAT TREATMENT

[0328] A solution of AAP (acrylic acid polymer) is prepared with 150 mg in 10 ml of ethanol. A solution of calixarene 49 is prepared with 11 g in 40 ml of DMSO (dimethylsulphoxide).

[0329] The final solution is made by adding 200 l of the solution of calix 49 into 10 ml of AAP solution. Stirring for 30 minutes is necessary in order to clarify the mixture.

[0330] A glass slide of the microscopy object slide type (7.52.5 cm) is coated in gold by a vacuum metallization process.

[0331] The application of the AAP solution onto the gold-coated slide is carried out by immersion-emersion in order to obtain after evaporation of the ethanol a homogeneous film of AAP that covers well, with a thickness of 70 to 100 nm. At this stage traces of DMSO are still present in the film.

[0332] The glass slides coated with AAP are then heated at 200 C. for 30 min in a simple oven at atmospheric pressure and without specific precautions. The DMSO is removed in this step.

[0333] FIG. 5 shows the results of the IR spectra recorded on the gold-coated slides at different stages of the process.

[0334] It is sought to detect the presence of calixarene in the AAP film. On the spectrum (a) which is recorded just after the deposition and drying of the alcohol, DMSO is also present (bands 1008 and 947 cm-1).

[0335] The bands corresponding to the calixarenes are faintly visible in particular at 1454, 1246, 1208, 1093 and 764 cm-1.

[0336] Spectrum (b) is recorded after baking at 200 C. The DMSO has disappeared. The bands corresponding to the calixarenes are still visible.

[0337] Spectrum (c) is obtained after hydrolysis for 10 minutes at pH=10.

[0338] Spectrum (d) is obtained with rapid rinsing of an initial film (equivalent to spectrum (a)) with water. Partial removal of the AAP is obtained and it becomes easier to observe the bands of the calixarene molecules which are relatively hydrophobic. This procedure makes it possible to increase the proportion of calixarene in the AAP films. This spectrum also shows that a significant proportion of calixarene is present in the film. With reference to the concentrations of the initial solutions of AAP and calixarene, the proportion on the spectrum (a) is 60 mg of calixarene for 150 mg of AAP.

EXAMPLE 5: PREPARATION OF THE AAP-CALIX-GOLD COMPLEX BY GAMMA RADIATION TREATMENT

[0339] A solution of AAP is prepared with 150 mg in 10 ml of ethanol.

[0340] A solution of calixarene 49 is prepared with 11 g in 40 ml of DMSO (dimethylsulphoxide).

[0341] The final solution is made by adding 200 l of the solution of calix 49 into 10 ml of AAP solution. Stirring for 30 minutes is necessary in order to clarify the mixture.

[0342] With reference to the dry compounds this represents 60 mg of calix 49 for 150 mg of AAP per millilitre of solution.

[0343] A glass slide of the microscopy object slide type (7.52.5 cm) is coated in gold by a vacuum metallization process. The application of the AAP solution onto the gold-coated slide is carried out by immersion-emersion in order to obtain after evaporation of the ethanol a homogeneous covering film of AAP with a thickness of 70 to 100 nm. At this stage traces of DMSO are still present in the film; prolonged natural drying, or even heating at 100 C./1 h is sufficient to remove the traces of DMSO solvent.

[0344] The glass slide coated with AAP+calix 49 is introduced into the irradiation chamber of a gammacell 3000 Elan with 662 keV photons (5.5 Gy/min). The irradiation lasts 8 h.

[0345] The immobilization of the coating is tested by washing abundantly with water or with basic solutions (ph=9-10). The film which is initially very soluble in water or the bases becomes insoluble and immobilized after irradiation.

[0346] Finally, the AAP film is immobilized on the surface after irradiation for 8 h. Radical cross-linking mechanisms have taken place within the volume of the film.